Problem: In language class, the girl to boy ratio is $7$ to $7$. If there are a total of $70$ students, how many girls are there?
A ratio of $7$ girls to $7$ boys means that a set of $14$ students will have $7$ girls and $7$ boys. A class of $70$ students has $5$ sets of $14$ students. Because we know that there are $7$ girls in each set of $14$ students, the class must have $5$ groups of $7$ girls each. There is a total of $35$ girls in language class.